Silicon carbide (SiC) is a high-hardness semiconductor material having a greater band gap than silicon (Si), and has been applied to various semiconductor devices including power elements, hostile-environment elements, high temperature operating elements, and high frequency elements. Among them, application to the power elements including switching elements and rectifier elements has drawn attention.
Metal-Insulator-semiconductor field-effect transistor (MISFET) is generally used as a power element. There is a case where a reflux current has to be allowed to flow in an inverter circuit, etc. when a power element is in an OFF state. In the case of a Si semiconductor, a body diode can be used as a path through which the reflux current is allowed to flow. However, when a forward current flows to a pn junction of a power element using SiC, stacking faults increases due to dislocations at the bottom of a substrate, which is a known problem unique to SiC (e.g., Patent Document 1). Therefore, it is difficult to use the body diode of the power element using SiC as a path of the reflux current, and thus a Schottky diode using SiC is generally externally attached to the MISFET in anti-parallel. However, when the Schottky diode is externally attached, the number of members increases, which also increases the area of the device. Moreover, even when the Schottky diode is externally attached, the power element using SiC may degrades if a reflux current flows through the body diode for any reason.
Thus, inventors of the present application have considered that a channel structure of a power element using SiC is optimized to form a portion functioning as a diode in a channel portion, thereby allowing a current to flow from a source to a drain without energizing a body diode (e.g., see Patent Document 2).